1. Field of the Invention
The present device relates to a bushed chain with rollers each fitted on the outside diameter of an oil-impregnated sintered bushing and, more particularly, to a bushed chain having rollers each fitted on the outside diameter of an oil-impregnated sintered bushing that chain life can be prolonged by decreasing a bearing surface pressure (pin outside diameter to bushing diameter) by increasing the pin outside diameter as compared with a proportion between component members of a standard chain.
2. Description of the Prior Art
Regarding a roller chain in conventional use, it has been a common practice to use a sintered oil-impregnated bushing for lubricating each chain-member bearing area and roller outside diameter where sprocket teeth contact when oil lubrication from outside is difficult or is not straightforward, thereby providing a self-lubricating mechanism. The efficacy and life of this self-lubrication mechanism is determined by the density of the sintered body and mechanical features such as mechanical strength, shock-resistance, elongation and fatigue strength. The volume of oil contained is determined with the volume of pores in sintered body, and the sintered density, if decreased, increases the oil content, providing the bushing with good lubricating properties but decreases the mechanical strength and toughness. Likewise, increasing the sintered density, increases the mechanical strength but decreases the oil content and decreases the lubrication quality and life.
From this point of view, attempts have been made such as the setting of a sintered density of sintered bushing low to contain more oil but not to decrease mechanical strength, or on the contrary set density of bushing high to obtain the high mechanical strength but sacrificing some portion of oil volume impregnated. Other attempts having included increasing the dimensions of the bushing to more than that of the common bushing as much as the roller dimensions reduced from the common chain rollers in order to increase the volume of the bushing to increase the volume of oil impregnated therein.
It is, however, impossible to simultaneously satisfy these characteristics which run counter to each other, and accordingly some consideration has to be incorporated in the design of each member for the purpose of maintaining these characteristics to some degree.
Meanwhile, from another point of view, it becomes necessary to prevent damaging the members at the time of installation of the entire roller chain. Namely, in the case of a small pin diameter, an outer link plate is fitted on the pin and "staking" the end of this pin is effected to prevent the accidental removal of this outer link plate. The pin diameter is increased larger than the bushing inside diameter by the "staking" and therefore is likely to impair the inner surface of the sintered bushing when the bushing is installed on the pin, sometimes breaking the bushing itself. Also, it is known to grind off the "staked" part by using a grinder prior to the linking of the chain. This method, however, will deteriorate characteristics of oil impregnated in the sintered bushing due to heat generated at the time of grinding, resulting in oil leakage and consequently in a decreased life of the chain itself.
Furthermore, when the pin outside diameter is small, an increased bearing surface pressure will result in decreasing or destroying wear resistance.